Image-forming apparatuses, e.g., copiers and printers, have in recent years been experiencing increasing diversification in their intended applications and use environments as well as demand for additional improvements in speed, image quality, and stability.
In addition, device downsizing and enhancements in energy efficiency are also occurring in copiers and printers at the same time, and magnetic monocomponent development systems that use a magnetic toner adapted to these trends are preferably used in this context.
In order for device downsizing and energy efficiency enhancements to coexist, it is essential to simplify not only the development structure, but to also simplify the fixing apparatus in the fixing structure. Simplification of the fixing apparatus can be achieved, for example, by using film fixing, which facilitates simplification of the heating source and the structure of the apparatus.
However, film fixing generally uses light pressures, and, when in particular the amount of heat is reduced with the goal of achieving an energy-saving fixing operation, an adequate amount of heat may not be obtained—depending on various factors such as the state of the surface of the media, e.g., the type of paper—and fixing defects may occur as a result.
When the goal is such a size reduction and energy conservation, an improved toner is desired that will enable a satisfactory fixing, regardless of the media, even in a light-pressure fixing step such as film fixing and that will thus enable the developing performance to coexist in balance with size reduction and energy conservation.
To respond to this problem, an improved low-temperature fixability and storability are pursued in Patent Literature 1 through the use of two release agents that exhibit different solubilities in the binder resin. However, room for improvement still remains here from the standpoint of the balance with image stability during durability testing.
An improvement in the offset resistance and fixing performance is pursued in Patent Literature 2 by controlling the state using an ester compound composed of a carboxylic acid and pentaerythritol or dipentaerythritol. However, room for improvement still remains here from the standpoint of the image stability during durability testing.
On the other hand, in order to solve the problems associated with external additives, toners have been disclosed with a particular focus on the release of external additives (refer to Patent Literatures 3 and 4). These have also not been satisfactory in terms of improving the low-temperature fixability of the toner.
Moreover, Patent Literature 5 teaches stabilization of the development • transfer steps by controlling the total coverage ratio of the toner base particles by the external additives, and a certain effect is in fact obtained by controlling the theoretical coverage ratio, provided by calculation, for a certain prescribed toner base particle. However, the actual state of binding by external additives may be substantially different from the value calculated assuming the toner to be a sphere, and, for magnetic toners in particular, achieving the effects of the present invention in terms of low-temperature fixability without controlling the actual state of external additive binding has proven to be entirely unsatisfactory.